VM-68 Full Auto Mod

The full automatic modification for the vm-68 will no longer be developed or sold by Alternative Paintball. Instead, as a treat to our loyal visitors, we will offer our designs to you for free! This mod will allow your VM to fire full auto as long as you hold back the trigger. Additional aftermarket parts are needed in addition to the auto mod in order for the paintball feeding to be fast enough for gun cycling. The following aftermarket parts are suggested before making your VM full auto:

bullet Pro Power Feed System
bullet Revolution agitating hopper.
bullet Large Volume CA system/Expansion chamber setup
The VM modified in this manner will not be select fire. Once in auto mode, to change back to semi will require trigger parts being replaced. The part only costs a few bucks, but it is a pain to replace!

You will need a bench grinder to complete the necessary modifications to the trigger mechanism.

Note: This modification is experimental. You may experience excessive ball breaks if your gun cycles too fast while firing full auto. Without the above add ons, you can not even hope to get your gun to fire effectively in full auto mode.

Instructions:

1. Remove any co2 charge from your gun. Unscrew the bottle from your gun. Tear your gun down to expose the lower bolt assembly. take out all springs, bolts and guides from the internals of your gun.
2. With all bolts and springs removed from the gun, look down the lower bolt chamber from the rear of the gun. You will see on the bottom of the chamber the primary sear. While looking down the chamber, pull the trigger back. You will see the primary sear drop down which would normally release the bolt had the gun been together. When the trigger is pulled back, the sear will drop and the secondary sear will be visible. It is a narrow flat piece of metal that sticks up in the chamber. When the bold slides forwards when firing, the lower bolt will push this secondary sear forward, disengaging it from the primary sear which will spring the primary sear back into the lock position position before firing). Now that you know the mechanics of the trigger mechanism, we may continue.
3. Remove the protective cover from the bottom of the grip frame. Using a long Allen head tool, unscrew the bolt that holds the grip to the gun. Remove the grip. This will reveal 2 more Allen head screws which hold the trigger assembly to the receiver. Unscrew these 2 bolts. When complete, the trigger assembly will drop away from the gun receiver.
4. Observe the trigger mechanism when detached from the gun. Watch the trigger action when you pull back the trigger. You will see the sear go up and down when pulling the trigger back and forth. Holding the trigger back, use your finger to push the secondary sear forward, disengaging it from the primary sear. You see how it allows the primary to pop back up? This action is what makes the trigger semi auto only. Release the trigger again and the secondary sear will engage the primary sear again, making it ready for the next shot. By shaving the top 1/4″ or so off the secondary sear, the bolt will not engage the secondary sear, allowing the bolt to cycle repeatedly as long as you hold back the trigger.
5. Shaving the secondary sear can be done by two methods, either by disassembling the entire trigger mechanism to remove the secondary sear, which I do not suggest you do unless you know how to put it back together, or just taking the entire trigger assembly to the bench grinder and carefully shaving the top portion of the secondary sear. Do not take off too much as the strength is still needed to hold down the primary sear when firing. Take a little off at a time and fit it back in the gun receiver to see if it still sticks up enough to be caught by the bolt. When the bolt slides past it freely, you have it shaved enough.
6. Once the secondary sear work is complete, reassemble the trigger mechanism to the receiver and reattach the grip. Leave all the bolts and springs out of the rear.
7. As it is now, your VIM will fire full auto, but most VM’s will cycle too fast that they chop paint. You may want to test fire your full auto vm before any other mods are complete. Reassemble your complete gun. If it doesn’t chop balls, your very lucky! But most VM’s need more work. Be sure to use an agitating hopper and power feed.
8. If your VM does cycle way too fast (likely), you will need to have it cycle slower. There is only one feasible way to accomplish this. The bolt travel must be adjusted so that it takes longer to travel back and forth in the receiver. Luckily, the VM is designed to very easily do this. Take your lower bolt assembly. Do you see the white plastic “bumper” on the rear? That one inch of space will slow the VM down quite a bit. Remove the white bumper by unscrewing the Allen head screw. Be careful not to lose any parts. The safety/cocking arm has a small ball bearing that is used as a detent to lock the cocking arm in the safe or fire mode. You will need to find a shorter screw to replace the one that held the white bumper in place and hold the rest of the lower bolt together.
9. Once the lower bolt is assembled without the bumper, put your gun back together and test fire in full auto. Try short bursts at first to see if you still chop balls. If not, kudos to you! Enjoy your new zero buck full auto mod. If you still have trouble with cycling, there is another way to achieve a slower cycle rate.
10. Remove all the bolts and springs again from your VM. When reassembling, do not use the spring guide on the upper spring. Also, do not use the bottom black metal plug that goes behind the lower bolt. This will give you about another 1/2″ of travel for the bolt.
11. You may notice that the cocking arm on the lower bolt is now what takes the brunt of the force when the gun recocks itself.(pull the lower bolt all the way back and you will see the cocking arm hits the end of the cocking arm slot. If the gun still cycles too fast, you will need to remove the cocking arm when firing so the bolt travels further. It just screws in from the outside of the gun, so installation and removal is not a problem. Just cock the gun, unscrew the cocking arm and your ready to fire.

Hopefully by now your gun cycling is slow enough so that balls will not chop. If you have all the above parts I listed that you need to add(hopper, feed, etc.) Then you should be ok. Each VM is different, some may cycle slower of faster than others depending on a variety of factors (co2 pressure, velocity, bolt drag, etc.) You may want to experiment with different settings for your vm(velocity) or even different upper bolts (oringless, oversized orings, etc) to get the right cycle rate. Now that you have the mechanics, it should be easy enough to tinker.

Good Luck!

Any questions or comments, leave us a comment! Let us know how your full auto VM came out!